使用合并排序对数组索引进行排序
Sorting index of array using merge Sort
我正在尝试使用合并排序对数组的索引进行排序。 mergesort 完美运行,最终答案完全正确,但我不确定为什么索引不能在正确的位置运行。我不想对数组进行排序,我只想对作为索引列表的 perm[] 数组进行排序。
为避免混淆,举个例子:
perm 数组保存原始数组 nums[] 的初始索引(即 0 到 nums.length - 1)
我想根据 nums[] 数组中的数据移动 perm 数组中的索引,以便索引代表排序顺序。
For example :
Array -> (-1,9,-5,3,0)
Initial perm -> (0,1,2,3,4)
After sorting perm based on array - > (2,0,4,3,1)
这是我的代码:
import java.util.Arrays;
public class IndexSort {
public boolean leq(Comparable u, Comparable v) {
return u.compareTo(v) <= 0;
}
public void merge(Comparable a[], int temp[], int perm[], int lo, int mid, int hi) {
int i = lo, j = mid + 1;
for (int k = lo; k <= hi; k++) {
temp[k] = perm[k];
}
for (int k = lo; k <= hi; k++) {
if (i > mid) {
perm[k] = temp[j++];
} else if (j > hi) {
perm[k] = temp[i++];
} else if (leq(a[perm[i]], a[perm[j]])) {
perm[k] = temp[i++];
} else {
perm[k] = temp[j++];
}
}
}
public void mergeSort(Comparable a[], int temp[], int perm[], int lo, int hi) {
if (hi <= lo)
return;
int mid = (hi + lo) / 2;
mergeSort(a, temp, perm, lo, mid);
mergeSort(a, temp, perm, mid + 1, hi);
merge(a, temp, perm, lo, mid, hi);
System.out.println(" lo = " + lo + " mid = " + mid + " hi = " + hi);
System.out.println(Arrays.toString(perm));
}
public void indexSort(Comparable nums[], int perm[]) {
int temp[] = new int[nums.length];
Comparable temp2[] = new Comparable[nums.length];
mergeSort(nums, temp, perm, 0, nums.length - 1);
}
public static void main(String[] args) {
IndexSort o1 = new IndexSort();
Comparable nums[] = { 12, -12, 0, 123, -123, 1, 2, 3, 4, -4, -4, -3, -2, 1 };
int perm[] = new int[nums.length];
for (int i = 0; i < perm.length; i++) {
perm[i] = i;
}
System.out.println(Arrays.toString(nums));
System.out.println(Arrays.toString(perm));
o1.indexSort(nums, perm);
System.out.println(Arrays.toString(perm));
}
}
我认为这一行需要从 perm
更改为 temp
:
} else if (leq(a[temp[i]], a[temp[j]])) {
我正在尝试使用合并排序对数组的索引进行排序。 mergesort 完美运行,最终答案完全正确,但我不确定为什么索引不能在正确的位置运行。我不想对数组进行排序,我只想对作为索引列表的 perm[] 数组进行排序。
为避免混淆,举个例子: perm 数组保存原始数组 nums[] 的初始索引(即 0 到 nums.length - 1)
我想根据 nums[] 数组中的数据移动 perm 数组中的索引,以便索引代表排序顺序。
For example :
Array -> (-1,9,-5,3,0)
Initial perm -> (0,1,2,3,4)
After sorting perm based on array - > (2,0,4,3,1)
这是我的代码:
import java.util.Arrays;
public class IndexSort {
public boolean leq(Comparable u, Comparable v) {
return u.compareTo(v) <= 0;
}
public void merge(Comparable a[], int temp[], int perm[], int lo, int mid, int hi) {
int i = lo, j = mid + 1;
for (int k = lo; k <= hi; k++) {
temp[k] = perm[k];
}
for (int k = lo; k <= hi; k++) {
if (i > mid) {
perm[k] = temp[j++];
} else if (j > hi) {
perm[k] = temp[i++];
} else if (leq(a[perm[i]], a[perm[j]])) {
perm[k] = temp[i++];
} else {
perm[k] = temp[j++];
}
}
}
public void mergeSort(Comparable a[], int temp[], int perm[], int lo, int hi) {
if (hi <= lo)
return;
int mid = (hi + lo) / 2;
mergeSort(a, temp, perm, lo, mid);
mergeSort(a, temp, perm, mid + 1, hi);
merge(a, temp, perm, lo, mid, hi);
System.out.println(" lo = " + lo + " mid = " + mid + " hi = " + hi);
System.out.println(Arrays.toString(perm));
}
public void indexSort(Comparable nums[], int perm[]) {
int temp[] = new int[nums.length];
Comparable temp2[] = new Comparable[nums.length];
mergeSort(nums, temp, perm, 0, nums.length - 1);
}
public static void main(String[] args) {
IndexSort o1 = new IndexSort();
Comparable nums[] = { 12, -12, 0, 123, -123, 1, 2, 3, 4, -4, -4, -3, -2, 1 };
int perm[] = new int[nums.length];
for (int i = 0; i < perm.length; i++) {
perm[i] = i;
}
System.out.println(Arrays.toString(nums));
System.out.println(Arrays.toString(perm));
o1.indexSort(nums, perm);
System.out.println(Arrays.toString(perm));
}
}
我认为这一行需要从 perm
更改为 temp
:
} else if (leq(a[temp[i]], a[temp[j]])) {